Hi - My '78 F-150 HAD two 351-Ms - the original (lower end went bad at about 80K) and then the one which came with it that the PO had partially installed. I finished up the installation, fired it up and it sounded like the oil pan was full of empty beer cans! Pulled that out, too and dropped in the 429. That was over 12 years ago. Big Blocks Forever!!!

 

All,
1. I've got a 78 F150 351M/FMX 4.10 rear end. It moves nice and idles fine, good oil pressure. Got headers... its loud.
2. Got a 78 F150 Supercab 400M/C6, don't know the gears. Its not running right now but it will someday soon. It's fast.
Life goes on....
KingFisher

 

351M here too.

I second that on the smooth idle. Sometimes when I come to a stop sign or light I think it stalled because it is so smooth and quiet. I sit there and rev it just to make sure its still running.

 

'77 F-150, 351 M, C-6, 205, 3.50 gears, 99,673 miles as I type this.

New rod and main bearings and oil pump at 75,000.

It does have Performer intake and 600 Holley and Crane Fireball cam and blue wires (lol).

Gets the same 12 mpg now as it did with Motorcraft 2bbl and factory flat cam and single exhaust, but it does run a bit better doing it.

Have 400 in basement, but have much body work and other stuff to do first.

Needs new rubber brake lines I see today as I installed new wheels and 31/10.50x15 Bridgestone H/L tires, so I ordered them to hopefully be here Tuesday. I don't take chances with brakes. The factory rubber lines were replaced in 1989, so these napa ones lasted longer.

 

351m here in my 79 250 custom. Still strong have no idea on miles or if it been rebuilt.

 

1978 F 250, 351M, np435, 2wd and 4.10 gears. has 117,000 miles and no rebuild. when i start it up it sits at 80 psi and after warrm up its at 5 psi. she runs strong , but i wish the rest of the truck looked better. hopefully get some body work done this summer. anyone know how to fix my oil pressure, or should i not worry about it. it scares me sometimes!!!

 

78RangerXLT,
I have a 79 F150 4X4 Short bed with a 4-speed trans. The truck has a 351M with 42K original miles on it. The engine runs fine with the exception of some valve clatter, which occurs under acceleration, why I am still not certain, and the annoying rear seal leak that leaves my garage floor a mess if I leave it sit too long.
John24255

 

I have an M in my 1979custom or will be this week, took the 300/6banger out, put in a windsor, blew it up, Now am installing the M block, added a performer manifold, some headers and a cam, freshened up nicely cant wait to get it fired up thrus or friday

 

i got a 79 f150 4x4 with a tired old 351M and a wore out t18. Got the motor out of a parts truck for $50. Ran great untill i blew the rear main seal and ran her low on oil a few times. she leaks about 3 quarts of oil every 50 miles!. but she always starts and still has ok power. whenever i get the 390 crank turned that's going back in.

 

78 351M posted "1978 F 250, 351M, np435, 2wd and 4.10 gears. has 117,000 miles and no rebuild. when i start it up it sits at 80 psi and after warrm up its at 5 psi. she runs strong , but i wish the rest of the truck looked better. hopefully get some body work done this summer. anyone know how to fix my oil pressure, or should i not worry about it. it scares me sometimes!!!"

Same problem I had at 75,000 all during a trip to Atlanta and back (1200 miles) ...
... answer was to set pick up up on sturdy jack stands in front, drop panhard rod, drop oil pan, replace rod and main bearings after determining that they were standard size (measured thickness of shell over on side at jointing surface where worn very little, not in center where copper was showing, machinist at NAPA shop checked book, it told size ... the numbers stamped in the bearing shell backs didn't help him or the FORD parts man)) and that crank surfaces were OK ... one bearing at a time. Be very careful not to let a rod hit the crank throw, just remove a cap, push out a upper shell towards tang, reinsert new, replace lower with new shell, put her back together, use new pan gasket.

New oil pump is a good idea too.

Mine was OK cold, but guage went to nothing when warm, and that's fast on the road. Thought was a sending unit, but after new sender didn't fix, I put a tube type guage on it back home ... 4 psi max when hot, which explained that rattle I noticed when I punched it in passing gear down near Chatsworth Ga.

I was very lucky. Now, at 100,025 miles ... it sits about 65 psi hot at 2500 rpm+, but in excess of 80-90 when cold if you just lightly increase rpms. I have a 100 psi Sunpro guage now, permanently installed.

 

I just put a 351M in my 1974 F-100. I pulled the 351 from a 1981 F-250 that had 74,000 original miles. Now I need to figure out how to wire it in since it has electronic ignition.

 

Two Years ago I bought a 1979 F-150 Supercab 4x4 with 115k miles on a 351m engine with noisy connecting rod bearings. After driving too long with this noise, Ihad two wholes in the block. I bought a rebuildt 351m shortblock(by Recon) and after all the work was done, I thought about saving money, while I´m driving my truck. So now it runs with LPG, which costs about the half of the regular gas. Still truckin´
Claus

 

79 F-150 351m auto. Truck isn't short on power, that's for sure, and quiet to boot. The 33" tires make more noise than the engine does!! As far as the power goes, it's a little less than our old 84 F-250 HD 460/4 speed.

Funny story about it. When Dad bought the truck a little over a year ago, he was told that it was a 302, and that the guy had just rebuilt it. Then, a few months later, the truck quit on us, about an hour and a half away from home (but luckily in the middle of a town, uphill from a gas staion and down the street from an autoparts store, not to mention the auto repair shop next to the gas station). He thought it was a bad fuel pump, so he went and got a new one for a 302. Didn't fit (different bolt pattern). He then told the guy what the pattern looked like, and he came back with one for a 351m. Turns out it wasn't the fuel pump, but rather the coil, so he got a new coil and found out what engine he had. Not the best way, but hey, it works.....

 

My 79 F-150 custom has a 351m. 144,000 miles, starts out cold with a high oil pressure and only goes down to about 40% on the guage when warm.

In the last few miles its had an Edelbrock intake/carburetor/timing chain, Summit cam, and valve springs updated. Water and oil pumps replaced because it was so easy at the time.

More than enough torque, and it will purr at idle. Will probably go past 200,000 without help. Starts on the first turn of the key assuming an electrical glitch hasn't drained the battery yet again...sigh.

 

I have two that are soon to be new 400's!!